1. Field of the Invention
The present invention generally relates to the field of telecommunications, and more specifically to the distribution of audio (voice, music, audio clips and the like) and/or video (e.g. video clips, movies) contents, e.g. multimedia contents, through telecommunications networks.
2. Description of the Related Art
Thanks to the technology evolution, the bandwidth available in telecommunications networks, using both fixed and mobile devices, has become broad enough to support the development of new services on a massive scale. Among this kind of services, the distribution of streams of audio and/or video contents, e.g. multimedia contents, is one of the most important. Streaming distribution of audio and/or video or multimedia contents is used for example for performing VoIP (Voice over Internet Protocol) phone calls, videocalls, for listening music through, e.g., Internet radio channels, IPTV (IP television), Video on Demand (VOD), content sharing.
In this context, an efficient usage of the available network resources and the ability to measure the quality of the services offered to the customers are important aspects and can determine the success for any player on the market; this is in particular true for telecommunications operators like Telcos, because they can leverage their own networks for providing these services.
The distribution of multimedia content streams in IP (Internet Protocol) network contexts requires to tackle many issues, coming from the specific context itself and from the users' perception and expectation; this information can be derived from the exploitation of similar services historically available in other domains.
The problem of measuring the quality of audio and/or video streaming distribution starting from the analysis of the network used for the provisioning and fruition of such contents has already been addressed in the art.
However, traditional methods of measurement, based on measuring network parameters without estimating the correlation among them, fail to estimate the quality of service from an end user point of view.
In order to estimate the true user's perception, it would be necessary to measure the quality of received content (audio, video, IPTV, VoIP, VOD, shared content) in the same or similar condition the user is when he/she is actually engaged in the content's fruition. This may not be possible by only measuring network parameters.
For example, measuring the available bandwidth is not a sufficient index of the quality perceived by the user during the content's fruition. A same degree of network performance degradation can have a completely different impact on the quality of the service as perceived by different users and in respect of different services, i.e. different distributed contents: for example, in the case of the vision of a movie, a high packet loss rate can be perceived by the users in a different way, depending on the movie's required bandwidth (if the required bandwidth is high, a high packet loss rate has heavier consequences on the users' perception than if the required bandwidth were lower).
Subjective methods known as “Mean Opinion Score” (MOS) (ITU Recommendation G.107—The E-model, a computational model for use in transmission planning P.910 “Subjective video quality assessment methods from multimedia applications”) provides for evaluating the perceived quality on a 0-5 range. However, this kind of methods is not useful for large-scale quality analysis campaigns, because they require the availability of trained people, giving uniform judgement through time (e.g. giving the same judgement about the same movie). Another problem in the application of this kind of methods is the impossibility of obtaining a diagnosis on errors' causes.
Better methods for large-scale quality analysis are those based on objective metrics, which have a well defined methodology whose results do not depend on the specific person making the analysis and whose values do not vary during time. A reliable method of estimation of the quality index should take into account the fact that some defects in the received stream are scarcely perceived, or not perceived at all by the users.
U.S. Pat. No. 7,197,557 discloses a system for measuring performance of streaming media sent from a server over a network. The system includes a data acquisition agent connected to the network and operable to send a request for streaming media to the server. The agent is configured to receive streaming media, collect performance measurements, and send the performance measurements to a storage device.
US 2007/053303 discloses a network performance monitor and an associated method for monitoring the perceived transmission quality of a packetized multimedia signal encoded by a first codec. The monitor includes a packet processor for performing real time direct counting of received and lost packets in the burst and gap states in the packet stream carrying the multimedia signal. A data processor is provided for determining packet loss distribution parameters using the burst and gap packet counters provided by the packet processor. The data processor is operative to compute an effective equipment impairment factor from the packet loss distribution parameters for a reference codec having known transmission impairments associated therewith, for assessing the network contribution to the perceived transmission quality of the multimedia signal.
U.S. Pat. No. 7,058,048 discloses a subjective quality monitoring system for packet based multimedia signal transmission systems which determines, during more than one interval of a single call, the level of one or more impairments and determines the effect of said one or more impairments on the estimated subjective quality of said multimedia signal. The quality monitoring system comprises a plurality of quality monitoring functions located at the multimedia to packet conversion points.
US 2006/190594 discloses a method and apparatus for determining the service quality performance of a real-time application, for example VoIP, video over IP or IPTV, operating over a path defined in a packet-based network. Active probing of a path of the packet-based network is performed by transmitting one or more sequences of packets along the path.